Red Hat Enterprise Linux is officially supported by Red Hat for 7 years. It's a better choice if you're running important machines in production, and you don't want to upgrade your OS all the time. It also has many nice features that are useful if you are running more than a few servers.

Also, you can (sometimes) actually call Red Hat and get support for RHEL, which you will never be able to do for Fedora.

Fedora is distributed for free, and RHEL costs money.

Fedora is much more cutting-edge than RHEL is, and Fedora has a larger community of users willing to help out and give free support.